1. Field of the Invention
This invention relates to a two directional pressure relief assembly for use in a fluid reactor system which has numerous advantages including the ability to act as a safety pressure relief device in either of two directions. That is, with the assembly hereof coupled to a reactor vessel, the assembly will relieve either an overpressure condition or an underpressure condition, with the assembly hereof allowing a large normal operating range in the reactor vessel.
2. Description of the Prior Art
In a chemical reactor system or similar application, it is usually necessary to provide some sort of safety device coupled to the reactor vessel to prevent a critical condition from occurring in the reactor vessel. Typically, such a critical condition has been an abnormal overpressure within the reactor vessel with the safety device operable to relieve the overpressure within the reactor vessel to prevent catastrophic failure. Conventional rupture discs are widely used in such applications, to prevent such a critical overpressure from occurring. That is, such conventional rupture discs are designed to burst at a predetermined pressure according to the needs of a particular application, and are coupled to the reactor vessel to burst and provide emergency pressure relief when the predetermined pressure is encountered.
In many reactor systems, however, it is necessary to not only provide emergency relief to prevent an overpressure from occurring, but additionally, it is necessary to prevent an underpressure from occurring. That is, in an integrated reactor system in which a particular reactor vessel operates under conditions dependent upon downstream or upstream conditions, it may be necessary to provide pressure relief when certain underpressure or overpressure relationship occurs between the particular reactor vessel and upstream or downstream conditions. For example, the normal pressure operating range for a reactor vessel might fluctuate relative to a downstream reactor vessel or system from 5 psi less than the downstream operating pressure to 5 psi greater than the downstream operating pressure (e.g. [-5 psi, +5 psi]). In such a system, it is desirable to provide emergency pressure relief when the operating pressure differential deviates either way from the normal range.
Similarly, many processes involve reactions with fluctuations of the reactor vessel pressure within a critical operating range irregardless of upstream or downstream conditions. It will be appreciated that this operating range can include pressures below atmospheric as well as elevated pressures. In such types of reactor vessels, it is therefore necessary to allow the vessel to operate in the normal operating range, but to prevent operation outside of that range, by monitoring the vessel pressure relative to atmospheric pressure.
One solution to protecting such a reactor vessel from both relative underpressure and overpressure has been simply to provide two conventional rupture disc assemblies, one for operation in an overpressure situation, and the other for operation in an underpressure situation. Although such a solution is effective in some instances, it will be appreciated that in many reactor systems because of cost constraints, space restraints, and/or the necessary pressure interdependencies within the integrating reactor system, this approach is not the most desirable or even feasible.
Another proposed solution to achieving full range protection for a reactor vessel has been to use one rupture disc assembly with two rupture discs mounted in the relief passageway connected to the reactor vessel. Such a device is illustrated in U.S. Pat. No. 3,091,359. In such devices, the rupture disc assembly typically comprises two perforated discs with an imperforate sealing membrane disposed therebetween. The downwardly bowed disc nearest the reactor vessel is designed to rupture as it reverses at a low pressure differential (underpressure condition), while the upwardly bowed disc on the other side of the sealing membrane, remote from the reactor vessel, does not undergo reversal and is designed to rupture at a high pressure differential (overpressure condition). In an underpressure situation, the pressure differential causes the membrane to distend against the lowermost disc, which bursts at its design limit to relieve the underpressure situation. Similarly, in an overpressure situation, the pressure differential results in distention of the membrane to a position against the upermost disc followed by bursting of the uppermost disc when the design pressure differential limit is exceeded.
A number of significant problems, however, exist with use of such past devices. First, in practice it has been found that the difference between the two designed burst pressure differentials for the two discs is somewhat limited. Thus, such past devices have not been effective in use with certain reactor systems which operate over relatively wide normal pressure ranges. Secondly, such past devices have not always been effective in providing the immediate full pressure relief necessary. Typically, this problem has manifested itself in the underpressure situation in which the lowermost disc ruptures, but the pressure is not high enough to rupture the uppermost disc which was designed to withstand a high pressure differential. Thus, the fluid must flow through the perforations in the uppermost disc which does not provide the full bore pressure relief which is desirable of not in fact essential to alleviate many abnormal operating conditions. Thus, a significant contribution to the art can be made by the provision of a single device which is capable of allowing operation of the reactor vessel over a wide pressure operating range and which provides immediate full bore relief when either a relative overpressure or underpressure condition occurs outside of the normal operating parameters.